An ink jet printer typically includes a printhead and a carrier. The ink jet printhead can comprise a printhead body, nozzles, and corresponding ink ejection actuators, such as heaters on a printhead chip. The actuators cause ink to be ejected from the nozzles onto a print medium at selected ink dot locations within an image area. The carrier moves the printhead relative to the medium, while the ink dots are jetted onto selected pixel locations, such as by heating the ink at the nozzles.
In some such systems, the ink reservoir comprises a removable or separable tank, such that the tank can be separated from the printhead, and replaced or refilled, when the ink is low. The printhead components can then be re-used. In such ink tank systems, a separable fluid connection between the tank and the printhead body is needed, in contrast to systems where the printhead body is integral with the ink reservoir. The connection permits ink to flow to the nozzles from the tank, but is separable such that the ink tank can be removed when empty.
The printhead assembly may also include a filter within an ink passageway leading from the ink reservoir to the nozzles, for isolating any contaminants or debris from the ejectors and nozzles. A chamber located between the filter and the nozzle is referred to as the ink filter tower as it contains ink after it is filtered.
The inks that are typically used for ink jet printing include dye inks and pigment inks. A significant problem associated with the use of pigment inks has been the settling of particles in the bottom of the main ink reservoir(s) of a printhead when a printhead sits idle for a while. This problem is especially pronounced with pigment inks that are designed to set quickly onto a printed surface. The settling of the ink can cause nozzles on the printhead to become clogged and malfunction and may produce lighter coloration on a printed document.
Various approaches have been considered to mitigate the settling problem within the main ink reservoir of the cartridge before the filter. One approach involves installing floating balls or rods in the ink reservoir that can roll around within the reservoir to stir the ink when the printhead moves. A simpler approach is to remove the printhead from the printer and shake it.
However, none of these approaches adequately address the settling of ink within a printhead that has an ink filter tower. The filter towers currently have no moving parts that can agitate the ink. Shaking the printhead is not particularly effective for this purpose. Moreover, the ink filter tower is of a very compact size compared to the size of the ink reservoir. It is therefore challenging to provide a suitable element for agitating the ink in an ink filter tower that would be effective and yet not get stuck and/or block the passageways through which the filtered ink flows to the nozzle.